> The difference is often less than a penny. But it adds up for larger trades. Schwab, for instance, says that for orders of 500 to 1,999 shares of S&P 500 companies, the average savings from price improvement is $10.80.

Ok and Schwab charges $4.95 for trades. So an investor ends up saving $5 per trade. S&P 500 companies stock price ranges from $20 to $1200 so to buy 500 shares of a company with $20 price per share would mean you spend $10000 resulting in a saving of 0.05%. On the other end of the spectrum you spend $600,000 resulting in a savings of 0.0008% assuming that when they say "average savings" they mean "average savings" per trade and not per share.

Just to put the whole thing in perspective.